STUDIES ON MONITORING AND PERSISTENCE OF COTTON/GRAIN PROTECTANT PESTICIDES UNDER ENVIRONMENT/ SIMULATED CONDITIONS AND THEIR EFFECTS ON FOOD CONSTITUENTS

Parveen, Zahida (1993) STUDIES ON MONITORING AND PERSISTENCE OF COTTON/GRAIN PROTECTANT PESTICIDES UNDER ENVIRONMENT/ SIMULATED CONDITIONS AND THEIR EFFECTS ON FOOD CONSTITUENTS. PhD thesis, University of Karachi, Karachi.

Abstract

COTTON: The data presented for cotton seeds clearly demonstrates an alternate and rapld procedure of analysis for fatty products at different levels of multiple residues of OC, OP and SP pesticides. Twenty-eight pesticides Including some metabolites had been Investigated. namely; aldrin, Y-SHC, blfenthrin chlorpyrlfos, cyfluthrin, cyhalothrin, cyhalothrin, deltamethrin, dlazinon, dicofol, dieldrin, dimathoate, DDT and Its metabolites, endosulfan, fenpropathrin, fenvalerate, flucythrinate, fluvalinate, heptachlor, methamldophos, parathion-methyl, pirimlphos-methyl and Profenofos. For Identification and determination, TSD/ECD d'3tector of Varian 3600 GC has been successfully employed. Two different column materials have been used for confirmation of the Identity of studied pesticides/metabolites.
Recovery studies for twenty-eight compounds were performed successfully In the cotton seeds. For each recovery attempt fortified and control sample were processed simultaneously. Recovery data as Indicated In table-IV of tested Pesticides/metabolites evaluated from the fortified cotton seeds ranged from about 79 to 99% of the samples. In addition, several SP additional pesticides which had not been found before were detected by the method employed. The described procedure thus proved to be quite efficient and sensitive and evidently provided satisfactory recovery of the tested pesticides from cotton seeds.
After having established proper analytical methodology, major cotton growing areas of Pakistan were surveyed extensively and 250 samples of cotton seeds were drawn from progressive farmer's field and different ginning factories. Thereafter, residues of parent pesticidal compounds and their metabolites were monitored In cotton seed samples In the laboratory.
73.60% samples were found to Le contaminated with 24 pesticides/metabolites. The results Indicate that out of 24 pesticides, 9 were OC's, 8 OP's and T were SP compounds. 40.84% of samples tested exceeded their respective MRL's. The most frequently occurring pesticides were cyhalothin, dimethoate, DDT and Its metabolites, endosulfan and monocrotophos. The presence of aldrin residues In cotton seeds of 1986-87 crop season reveals either Its massive application In the past for control of agricultural pest or during Invasion of locust swarms. References are replete In literature from around the world confirming this situation when aldrin/ dieldrin were largely used In agriculture. The other probability is that some farmers hoarding the stock of this persistent OC, have used It as an element of insurance to protect his cotton crop.
WHEAT: There Is only a small armoury of compounds that are considered safe enough to admix with stored grains. Because of resistance and other factors like persistence, etc. two pesticides of OP and one of SP group were chosen for the present study. The accuracy and reproducibility of analytical methods for the assay of these grain protectants have been investigated. Results were assessed using data from trial applications of chlorpyriphos-methyl, pirimiphos-methyl and permethrin pesticides, applied directly to wheat grains and stored at two moisture content levels and a t four different temperatures In the laboratory. This was done With a view to simulate different climatic zones of this country.
A total of 1152 samples of treated wheat with above mentioned three pesticides with an additional 384 control samples were drawn from storage at regular Intervals. Each sub-sample was analyzed for residues in tripilicate. Alongwith control samples according to procedure described in the experimental section. The sample was ground to a coarse powder, extracted with suitable solvents, cleaned up and finally assayed for residues by gas chromatography using thermionic specific and electron capture detectors. Rates of loss were calculated from the results obtained The decline in. concentration of these residues on stored wheat was o maximum at 40C and at 13% moisture content whereas it was o minimum at 25C and 10% moisture content. Amongst the three, pesticides, permethrin was found to be the most persistent one ,followed by pirimiphos-methyl while chlorpyriphos-methyl was found to be the least persistent one. Permethrin, a pesticides, of S P group, which consists of a mixture of cis- and trans-Isomers, loses the trans-Isomers more rapidly, as evident from Its gas chromatograms.
Pseudo first-order rate constants for rate of loss of these pesticides on stored wheat under controlled environment were calculated In accordance with the equation given In the section of persistence studies. The tables and figures relating half-lives of the pesticides to moisture contents, temperatures and rate-constants are presented in a form, suitable to assess the degradation rate.
In this country, where grain protectant pesticides are used exclusively and extensively for the protection of wheat and other grains, the present study confirms that the Intake of the residues of the above mentioned OP pesticides in food commodities such as wheat to whole meal, wheat to white flour, wheat to whole meal bread and wheat to white bread, is within the ADI levels prescribed even after nine months' storage period at high temperature and high moisture content levels, while In case of residues of the SP pesticides, only white bread is consumable after storage of treated wheat for six months at 40 C and at both the moisture content levels as Its ADI (0.05 ppm) is higher than the other two pesticides (0.01 ppm). The mechanism of pesticides' degradation during processing may be attributed mainly to evaporation and thermo-decomposition. The higher the moisture contents, the more pesticide residues will be lost during the manufacturing processes as it is evident from permethrin behaviour which can be consumed even after post treatment storage period of 3 months at higher moisture levels. Therefore in the study of behaviour of pesticide residues in grains, the factors discussed in previous section are considered integrally vital.
FOOD-CONSTITUENTS: In this 'section' the effects of studied pesticides on food constituents in cotton seeds and wheat grains have been evaluated. The results are assessed using analytical data from trial application of the OC, OP and SP pesticides directly to the aforesaid food commodities and the studied samples were stored at room temperature (30oÃÂÃÂÃÂÃÂ±3C) for one month in sealed glass Jars. Each of the sample was analyzed for macro- and ml cro-.food constituents in triplicate along with control samples.
The studies on the effects of the pesticides on carbohydrates, lipids, proteins, phosphorus and trace metals were carried out successfully in both the food commodities. This study indicates that the aforesaid pesticides generally cause reduction of carbohydrates, while, the application of monocrotophos (OP) on cotton seeds and pirimiphos-methyl (OP) on wheat grains increased the lipid contents. On the other hand the OC and SP pesticides decreased the protein contents while OP pesticides increased in appreciable quantities in both the commodities. The influence on amino acids, analyzed by amino Acid analyzer, was noted to be variable. The essential content, phosphorus, was observed to h3ve increased quantitatively by the application of OP pesticides. The trace metals in control samples of each commodity were present in normal range, which are essential for a healthy seed. It may thus be summed up that the pl1stlcldes tested in this context generally effect adversely the food constituents In both the food commodities.